Heads can give permission for children to be absent for up to 10 days of a school year - for example if parents cannot take leave during the summer, but Mr Lewis said term-time holidays should be "the exception, not the rule".

The Department for Education and Skills (DfES) has teamed up with the Association of British Travel Agents (Abta) to urge parents in England to book family trips in official school holidays. With the industry gearing up to sell next year's summer breaks, ABTA has told its members to remind parents of the rules.

It is up to the head to decide whether or not to grant permission for a child to be absent during term time.

Under the Anti-Social Behaviour Act that was passed by Parliament recently, heads will have the power to issue on-the-spot fines of up to £100 to parents of children who play truant.

The fines are primarily intended to bring parents who repeatedly let their children miss school to their senses as an alternative to prosecution and a possible prison sentence.

But the DfES stressed that fines could be handed out for a first-time offence in "exceptional circumstances, for example where a parent has taken their child on holiday in term time without the school's permission". However, it is debatable whether many parents will be fined for such transgressions, as heads have neither demanded nor welcomed their power to impose them.

And the Government's warning is likely to annoy parents who believe travel firms exploit the rules by hiking the price of package deals during school holidays.

Mr Lewis said: "Taking a holiday during term time can mean that children miss important school time and coursework and it will be difficult for them to catch up later on."

Abta chief executive Ian Reynolds said: "Our members always encourage families to book early by providing excellent early discounts and free child places for what are always busy school holiday periods.

"Booking now means getting holidays at a good price, getting maximum choice and also means that your children's education doesn't suffer."